Anti-psychotic drugs act synergistically in combination with antifungal drugs to inhibit drug-resistant Cryptococcus neoformans and Candida albicans

ABSTRACT Systemic fungal infections cause an estimated 3.8 million deaths annually, approximately 10% of which are caused by drug-resistant infections. With only five classes of antifungal drugs, treatment options are limited. Here, we explore synergistic drug combinations—when the efficacy of two drugs combined is greater than expected based on the sum of each individual drug’s efficacy—to improve treatment of drug-resistant Cryptococcus neoformans and Candida albicans . Chlorpromazine acts synergistically with both amphotericin B and fluconazole against multiple fungal species, including azole-resistant C. neoformans and C. albicans . We then performed a genome-wide knockout mutant screen and found that ESCRT pathway mutants are resistant to chlorpromazine, while knockout mutants of genes involved in fatty acid biosynthesis are sensitive. Based on these data, we investigated sterol and fatty acid composition in chlorpromazine-treated cells and found only minor increases in sterol precursors, but a substantial increase in lipid droplet size and decreased lipid droplet numbers. This lipid droplet formation potentially sequesters lipid bioavailability and response to membrane stress. Together, these data suggest that chlorpromazine and its analogs are potentially promising treatments for systemic fungal infections that act via lipid homeostasis and stress response. IMPORTANCE Fungal infections are a large and expensive health burden with high mortality rates. People with compromised immune systems from cancer, solid organ transplant, HIV infection, and other conditions are particularly affected. Systemic fungal infections are difficult to treat because there are few available drugs and treatment periods last months or years. Long treatment times increase the risk of treatment failure and can contribute to the rise of resistance. We identified an additional class of drugs, chlorpromazine and other phenothiazine drugs, that amplify the activity of existing antifungal drugs amphotericin B (AmB) and fluconazole (FLZ). AmB and FLZ act by targeting ergosterol, the fungal equivalent of cholesterol, which is required for a functional plasma membrane. Chlorpromazine increases the formation of lipid drops, which sequester lipids such as ergosterol. When chlorpromazine is combined with AmB, the fungal cell cannot respond to the plasma membrane damage caused by AmB, inhibiting the fungal cells. This work identifies new target processes and drugs that could treat deadly fungal infections.